Wiktionary
n. A very close friend.
Usage examples of "bosom buddy".
One minute you'll be the savior of the rebel cause, then, next thing you know, you'll be Cohaagen's bosom buddy.
Two minutes later and your bosom buddy Garcia would have had you in bracelets.
His bosom buddy of course took a wide sloppy swing at Krome's noggin, but Tom had plenty of time to duck (Mary Andrea was way ahead of him) and unleash a solid uppercut to the scrotal region.
If it was someone from the same colony, it was like meeting a bosom buddy.
While he didn't suppose Lieutenant Basingstoke was going to become a bosom buddy, at least he knew his job.
How had she convinced Gadbois to free him and not keep his bosom buddy, Owen Glendenning, in the loop?
Then he picked up Chriss dirty kit and carried it to the car while Chris shook hands with his new bosom buddy.
Ever since the clash of loyalties had come out my way on the world in the Drift, Nick had reckoned himself my bosom buddy.